Handle new DamageUnregister API which has only one argument

API change in 1.15

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
Merge pull request #2 from grate-driver/issue-1-fix

Handle new DamageUnregister API which has only one argument